Method for fabrication of precision miniature glass circuits

ABSTRACT

Precision miniature glass circuits, such as fluidic circuits and optical waveguide and laser circuits, are fabricated by assembling a plurality of glass members of at least two differing types of glass to form a subassembly. The subassembly is heated to fuse the glass members together. The cross sectional dimensions of the assembly may be reduced by drawing. The fused assembly is sliced to obtain a plurality of slabs, each having the two types of glass therein with one of the types of glasses defining a circuit pattern for flow of energy, such as fluid energy or optical energy, therealong. In the case of fluidic circuits, the glass type which defines the circuit pattern is etchable so that it can be removed to provide the fluid flow circuit passageways in the slab. In the case of optical waveguides and circuits, the type of glass defining the circuit pattern has a different index of refraction from the other glass members in order to form light paths or pipes. The slabs containing the circuit patterns are sandwiched between pairs of glass slabs for providing strength and/or for closing off the opposite sides of the energy flow circuit patterns.

ESQ-96.12 5H 7 r me. XR I 397714983- 3 111 3,771,983 Straka l Nov; It1973 METHOD FOR FABRICATXON OF PRECISION MINIATURE GLASS CIRCUITS [57]ABSTRACT l lnvemori Emil simka San Jose, Calif Precision miniature glasscircuits, such as fluidic circuits and optical waveguide-and lasercircuits, are fab- A'flvr' A 't,PlAlt,Cl'f. I 3] sslgnee a an Ssoua es aO O a ricated by assembling a plurality of glass members of Filcdl J1971 t at least two differing types of glass to form a subassembly. Thesubassembly is heated to fuse the glass [21] Appl' 156211 memberstogether. The cross sectional dimensions of the assembly may be reducedby drawing. The fused i 1 Cl 65/31, 65/4, 65/56. assembly is sliced toobtain a plurality of slabs, each /DlG. 7, l56/3, 156/15, 156/17. 156/24having the two types of glass therein with one of the [51] Int. Cl CUBC15/00 types of glasses defining a circuit pattern for flow of [58] Fieldof Search 65/31, 42, DIG. 7, energy, su h as fluid energy or opticalenergy, there'- 5/ 156/3. 5 101 along. In the case of fluidic circuits,the glass type which defines the circuit pattern is etchable so that itl References Cited can be removed to provide the fluid flow circuit pas-UNITED STATES PATENTS sageways in the slab. ln thecase of opticalwaveguides 3,275.428 9/1966 Siegmund 156/24 x and Circuits, the W ofglass defining the Circuit P 3 29 386 1/1967 vevoda H 156/299 X tern hasa different index of refraction from the other 3.331757 7/1967 Hawkins65/31 x gl m mber in order o form light paths or pipes. 3.-155,6677/1969 Snitzer etal 65/56 The slabs containing the circuit patterns aresand- 5668 /1969 Upton 65/61 wiched between pairs of glass slabs forproviding 35021455 3/1970 Gardner 65/61 strength and/or for closing offthe opposite sides of the energy flow circuit patterns. PrimaryExaminer-Robert L. Lindsay; lr. M Armrney-Stanley Z. Cole 3 C 9 nrfiwmgllgul'es mmmuvas ma 3.771.983

v INVENTOR.

EMIL R. STR'AKA w gQak. i

ATTORNEY METHOD FOR FABRICATION OF PRECISION MINIATURE GLASS CIRCUITSDESCRIPTION OF THE PRIOR ART Heretofore, it has been proposed tofabricate precision miniature glass circu'its, such as fluidic circuitsand optical waveguide circuits, by any one of a number of differentmethods such as machining, photoetching, or diffusion. The problems withthese priormethods are that they are either relatively imprecise or areextrcmely expensive and complex for obtaining circuit dimensiontolerances on the order of one-tenth ofa micron or less. Such prior artmethods for fabricating precision miniature optical circuits of glassare disclosed in the Bell System Technical Journal, Volume 48 ofNovember 7, I969, inarticles titled Integrated Optics: An Introduction,and Dielectric Rectangular Waveguide and Directional Coupler ForIntegrated Optics."

SUMMARY OF THE PRESENT INVENTION tioned to form an assembly which isheated to fuse the different glass members together. The fused assemblyis sliced to obtain at least one slab of glass having the two types ofglass therein with one of the types ofglass defining a circuit patternfor flow'of energy therealon-g, whereby precision miniature circuits ofglass are readily fabricated.

In another feature of the present invention, the assembly of glassmembers of differing types is heated and drawn to reduce the crosssectional dimensions of the assembly to further reduce the size of theresultant glass circuits.

In another feature of the present invention, the one type ofglass whichdefines the circuit pattern in the cir- -cuit slab has an index ofrefraction sufficiently different than the index of refraction of theother type of glass such that the circuit pattern formed in the slabdefines an optical waveguide.

In another feature of the present invention, at least one of theassembled types of glass is more readily e'tehablethan the other type ofglass and defines a glass circuit pattern in the slab. The etchableglasspattern is suitably removed (cg; chemical etch, sputter etch, ultrasonicetch) to define a circuit pattern of fluid flow passageways for flow offluid energy there-through.

In another feature of the present invention, a glass slab having thecircuit pattern defined therein is joined along at least one of itsmajor faces to a second glass slab to improve the strength of theresultant assembly, or to provide appropriate boundary conditions forthe conduction of energy.

In another feature of the present invention, a glass slab containing thecircuit pattern is joined between a pair of glass slabs to form awherein: glass sandwich.-

Other features and advantages of the present invention will becomeapparent upon a perusal of the follow ing specification taken inconnection with the accompanying drawings, wherein;

BRIE-F DESCRIPTION OF THE DRAWINGS FIG. I is a schematic perspectiveview depicting an assembly of glass members of differingcharacteristicsin the first step in the method for fabricating precision miniatureglass circuits according to the present invention,

FIG. 2 is a schetnatic perspective view of the assembly of FIG. 1depicting a slicing operation wherein the fused assembly is sliced intoindividual glass slabs according to another step in themethodof thepresent invention,

3 is a schematic perspective view of a slab containing a glass circuitjoined to a supporting slab of glass in accordance with another step inthe method of the present invention,

FIG. 4 is an enlarged perspective view of the structure of FIG. 3 afterappropriately removing the glass circuit pattern formed by the unstableglass according to another step in the method of the present invention,FIG. 5 is an enlarged perspective view of the structure of FIG. 4including a second slab of glass joined to the top'of the assembly ofFIG. 4 to define a fluidic circuit, I

' FIG. 6 is a view similar to that of FIG. I depicting a similar stepfor forming an optical circuit of glass,

FIG. 7 isa view similar to that of FIG. 2 depicting a slicing step inthe method for fabricating an optical circuit,

FIG. 8 is a view similar to that of FIG. 3 depicting joining the glasscircuit slab to a substrate slab, and

FIG. 9 is a view similar to that of FIG. 5 depicting the last step inthe method of forming the optical circuit wherein a second glass slab isjoined to the top of the circuit.

DESCRIPTION OF PREFERRED EMBODIMENTS method of the present invention forfabricating precision miniature fluidic glass circuits. In the firststep of v the method, which is depicted in FIG. I, a bundle of glassmembers are assembled. The glass members are of at least two differingtypes of glass. For example, in the case for fabrication of fluidiccircuits, certain ones of the glass members are made of a glass which isreadily chemically etched, such as Schott glass, type LAX- 3commercially available from the Schott Glass Companyof Duryea,Pennsylvania. This chemically unstable glass is arranged in a certainpredetermined pattern within the bundle of glass such that a crosssection through the bundle will show the chemically etchable glassarranged in a pattern conforming to the fluidic circuit pattern to beformed. The remainder of the bundle is made of a second type of glasswhich is chemically more inert. An example of such'chemically inertglass includes glass sold under the trademark Pyrex by' Corning GlassWorks, Corning, New York. One suitable glass utilizable with Schottglass is Coming glass No. 8161. The first and second types of glassshould have similar thermal expansion characteristics, and the secondtype glass should have a higher viscosity than the first type in thetemperature range at which they will be worked, as by drawing. Forexample, a difference in softening temperatures of IOOC is appropriate.The bundle of glass I is assembled within a suitable mold (e.-g.,carbon) and held therein to retain the proper shape. The individualglass members have preformed desired cross sectional shapes obtained forexample by prior drawing. The carbon mold is then inserted into afurnace preferably having an inert nitro- Referring now to FIGS. 1-5,there is depicted a gen atmosphere and raised to a sufficienttemperature to fuse or tack the various glass members of the bundletogether to form a rigid fused bundle. Typically, tacking occurs at atemperature of approximately 100C below the softening point of theglasses.

In the third step of the method, the fused bundle of glass, as shown inFIG. 2, is removed from the mold and sliced into slabs by means of asuitable saw such as a wire saw or band saw, to form individual slabs 2.Each slab 2 contains the pattern of unstable glass which is to definethe tluidic circuit.

In the fourth step of the method, the major faces of the individualglass slabs 2 are lapped and polished and one is placed in intimatecontact over a second slab 3 of glass of a type corresponding to thestable glass type.

The sub-assembly is then inserted into a furnace and heated to-atemperature slightly above the tacking ternperature and slightly belowthe softening point to fuse the circuit slab 2 tothesupporting slab 3.

In the fifth step of the method, as shown in FIG. 4, the unstable glassis etched away to form the subassemb'ly of FIG. 4 by immersing thesub-assembly in a suitable etchant, such as hydrochloric, nitric, oracetic acid. Etching is continued until the unstable glass has beenremoved.

In the sixth step of the method, as shown in FIG. 5,

a second slab of stable glass 4 is fused over the top of the etchedfluidic circuit in the manner as previously described above with regardto the fourth step of the method. A port 5 may also be provided in thecover plate 4 to provide a signal or gating input of flow of respondingincrease in the length of the bundle. Several bundles may then beassembled in the proper relationship to define a multiple stage fluidicamplifier circuit. The multiple stage fluidic amplifier circuit bundleis then fused in the same manner as previously described with regard toFIG. 1 and the fused or fused and drawn composite assembly is thensliced and fused to plates as previously described with regard to FIGS.25 to provide a composite fluidic amplifier circuit. In eachdraw ingstep the cross sectional dimensions may be reduced by a factor of 10 to20.

Referring now to FIGS. 6-9, there is shown a method substantially thesame as that previously described with regard to FIGS. 1-5, forfabricating precision miniature optical waveguide circuits or lasercircuits, and, in particular, an optical directional coupler. Moreparticularly, in the first step of the method, as shown in FIG. 6, abundle of glass members is assembled of two types of glass havingdifferent indicesof refraction and viscosities but similar lightattenuation properties and coefficients of thermal expansion. Forexample, those glass members which are to form the optical waveguidecircuit are formed of a glass having an index of refraction between 0.01and 0.05 greater than the index of refraction of the-glass whichis toform the body or noncircuit portions of the directional coupler. Forexample, a suitable glass which is to form the optical waveguide circuitis Schott LA I(3, commercially available from Schott Glass Company ofDuryea, Pennsylvania,

such glass having an index of refraction of 1.693, whereas the glassforming the body portion may comprise Corning Glass No. 8 1 ol having anindex of refrac tion of 1.659 and is commercially available'from CorningGlass Works of Corning, New York.

In the second step, the glass members are fused, or fused and drawn in adrawing. furnace. In a typical example, the drawing furnace may have afeed rate of x and the bundle may be drawn out of the furnace at a drawrateof 10 to 20 times x to produce a substantial reduction in the crosssectional dimensions of the bundle being drawn. As previously mentionedabove, the

drawn membersmay then be assembled into another assembly and fused ordrawn a second time to produce even smaller and more intricate circuits.

The fused bundle of glass members is sliced on a wire saw or band saw,as aforedcscribcd, to produce individual glass slabs 2 containing theoptical circuit pattern therein of the glass of higher index ofrefraction. The slabs 2 are then lapped and polished by standardprocedures to an appropriate thickness, 0.010 to 0.015 inch with anoptical lapping compound and polished with 1 micron cerium oxide. Thelapped and polished slabs 2 are fused to a supporting glass slab 3 whichmay be chosen for certain special properties or it may be the same glassas that of the body of the slab 2 which contains the circuits.

In the next step, additional polishing of the topside of the fused slab2 and support 3 is obtained to allow the original-circuit slab layer 2to be polished to an overall thickness corresponding to a desiredoptical waveguide height or thickness. Typical waveguide heights obtainable by this method range down to 0.5 micron, which is suitable forvisible light,

In the final step of the method, as shown in FIG. 9, an additional slabof glass-4 is fused over the polished vtop surface of the opticalwaveguide circuit to provide asandwich of glass which includes thedirectional cou- .pler circuit.

A variety of other optical devices which may be fabricated according tothe method of FIGS. 6-9 include di rectional coupler hybrid resonators,straight channel dropping filters, junction hybrids, ring and pill boxchannel dropping filters, and with the use of diffusion and ionimplantation mentioned in the aforecited Bell System Technical Journal,phase and amplitude modulators, 'detectors,-light sources andamplifiers.

The advantage of the method of the present invention for fabricatingprecision "miniature glass circuits, such as fluidic or opticalcircuits, is that the circuits may be readily fabricated with extremelyclose tolerances, such as one-tenth of :1 micron or less. Drawing theglass bundles allows the circuit proportions to be determined withrelatively large glass members. These proportions are retained while thescale of the circuit is reduced by drawingto extremely small dimensions,as aforedescribed.

As used herein "glass" is defined as including glass like materials suchas glassy systems, fused quartz, and ferro-eleetric glass ceramicsystems such as those disclosed in an article by N.F. Borrelli et al.,appearingin The Proceedings of the Toledo Award-Symposium of TheAmerican Ceramic Society, January 18, I971.

lnthe case of fluidic circuits, the etchable glass need only besubstantially more rapidly etchable than the other glass. Suitableetching methods include chemical etching, sputter etching and ultrasonicetching.

in the case where a cizcuit slab portion is joined to a supporting orcover slab, the slabs necd not be joined by fusing, but may be joined bya suitable adhesive. in the case of an optical circuit, an opticalcement having the appropriate index of. refraction would be employedAlternatively, a fluid layer, as of gas or liquid, ofproper index ofrefraction could join the circuit slab to the supporting slab.

in the aforedescribed optical waveguide embodiments, othersuitablecombinations of glasses include Schott Glass No. SK- 19, which would beused for the light path while BaLF4 is suitable as the body portion ofthe composite glass structure. What is claimed is: l. A method forfabricating circuit devices of glass comprising the steps of:

positioning at least three elongated glass members of uniform crosssection together such that one of said members is positionedintermediate the other two and said members are oriented in a givendirection, the intermediate one of said members having a differcnt etchresistance than the other two of said members, heating said members tofuse them together to form a first assembly, the shapes of said membersbeing slicing a cross-sectional portion from said first assembly toobtain a first slab having two major faces,

joining one of the major faces of said first slab to a bottom glass slabto form a second assembly,

subjecting said second assembly to an etchant which will remove onlysaid intermediate member,

joining the remaining, exposed major face ofsaid first slab to a topglass slab such that said bottom and top slabs sandwich said second andthird glass members and such that the void left by the removal of saidintermediate glass member provides a. circuit path bounded by said othertwo glass members and said bottom and top slabs.

2. The method of claim 1, further including the step of drawing saidfirst assembly of glass members to reduce the corss-sectional dimensionsthereof prior to slicing said first assembly.

3. The method of claim 2, further including the step of polishing saidcross-sectionalslab after it is sliced from said first assembly.

1. A method for fabricating circuit devices of glass comprising thesteps of: positioning at least three elongated glass members of uniformcross section together such that one of said members is positionedintermediate the other two and said members are oriented in a givendirection, the intermediate one of said members having a different etchresistance than the other two of said members, heating said members tofuse them together to form a first assembly, the shapes of said membersbeing such that in a cross-sectional view of the fused assembly, theboundaries of said intermediate member with said other two membersdefine a circuit path perpendicular to said given direction, slicing across-sectional portion from said first assembly to obtain a first slabhaving two major faces, joining one of the major faces of said firstslab to a bottom glass slab to form a second assembly, subjecting saidsecond assembly to an etchant which will remove only said intermediatemember, joining the remaining, exposed major face of said first slab toa top glass slab such that said bottom and top slabs sandwich saidsecond and third glass members and such that the void left by theremoval of said intermediate glass member provides a circuit pathbounded by said other two glass members and said bottom and top slabs.2. The method of claim 1, further including the step of drawing saidfirst assembly of glass members to reduce the corss-sectional dimensionsthereof prior to slicing said first assembly.
 3. The method of claim 2,further including the step of polishing said cross-sectional slab afterit is sliced from said first assembly.